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Diffstat (limited to 'kernel/sched/idle.c')
-rw-r--r--kernel/sched/idle.c26
1 files changed, 25 insertions, 1 deletions
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 25b9423abce9..fe4b24bf33ca 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -67,6 +67,10 @@ void __weak arch_cpu_idle(void)
* cpuidle_idle_call - the main idle function
*
* NOTE: no locks or semaphores should be used here
+ *
+ * On archs that support TIF_POLLING_NRFLAG, is called with polling
+ * set, and it returns with polling set. If it ever stops polling, it
+ * must clear the polling bit.
*/
static void cpuidle_idle_call(void)
{
@@ -175,10 +179,22 @@ exit_idle:
/*
* Generic idle loop implementation
+ *
+ * Called with polling cleared.
*/
static void cpu_idle_loop(void)
{
while (1) {
+ /*
+ * If the arch has a polling bit, we maintain an invariant:
+ *
+ * Our polling bit is clear if we're not scheduled (i.e. if
+ * rq->curr != rq->idle). This means that, if rq->idle has
+ * the polling bit set, then setting need_resched is
+ * guaranteed to cause the cpu to reschedule.
+ */
+
+ __current_set_polling();
tick_nohz_idle_enter();
while (!need_resched()) {
@@ -218,6 +234,15 @@ static void cpu_idle_loop(void)
*/
preempt_set_need_resched();
tick_nohz_idle_exit();
+ __current_clr_polling();
+
+ /*
+ * We promise to reschedule if need_resched is set while
+ * polling is set. That means that clearing polling
+ * needs to be visible before rescheduling.
+ */
+ smp_mb__after_atomic();
+
schedule_preempt_disabled();
}
}
@@ -239,7 +264,6 @@ void cpu_startup_entry(enum cpuhp_state state)
*/
boot_init_stack_canary();
#endif
- __current_set_polling();
arch_cpu_idle_prepare();
cpu_idle_loop();
}